Method of making electron-emitting cathodes



Sept. 5, 1939. E. H. WITTICH 2,172,326

' ELECTRON-EMITTING c E E5 Filed Spt. 28, 1936 Patented Sept. 5, 1939 UNITED A STATES METHOD OF MAKING ELECTRON-EMITTING CATHODES Edward H. Wittich, Beverly, Mass., mm. to Hygrade Sylvania Corporation, Salem, Masa, a. corporation ofMassachusetts Application September 28, 1936, Serial No. 102,894

Claims.

This invention relates to electron-emitters and more particularly to methods for providing such emitters with their electron-emissive coatings.

Heretofore, electron-emissive coatings have 5 been applied to filaments and cathode sleeves or the like by spraying or by the so-called cupping process, the latter process requiring the employment of a series of cups containing the coating material and through which the filament to be coated is'successively passed. The spray process however entails certain disadvantages, the most pronounced of which is the difiiculty of securing uniformity of coating. This difiiculty is further accentuated in connection with It so-called indirectly heated cathodes employing a tubular metal sleeve, because the cupping process is not feasible as applied to this type of cathode, and resort must be had to spraying. However, even when such" cathode sleeves are 20 sprayed, it is extremely diflicult to control the uniformity of coating because of a number of factors requiring control including density of the spray, clogging of the spray-gun, different sizes 01' sleeves to be coated, and maintenance of as proper temperature, humidity and cleanliness of the spray compartment. Ancillary to the above- -noted difficulties is the waste of material during spraying, particularly when it is considered that the usual cathode sleeve is of relatively minute 36 dimensions and in order to utilize the spray process it is necessary to position the sleeve in a cloud of spray. Thus, the spray process ordinarily results in non-uniformity of coating not only along the length and circumference of each :5 cathode, but even successively sprayed cathode sleeves will vary among themselves thus militating against the desired uniformity of operation in the finished tubes.

Accordingly one of the principal objects of 40 this invention is to provide a method to coat bodies whether of the filamentary or tubular sleeve type, whereby uniformity of electron-emissive coating is obtained.

In certain cases it is desirable to be able to 48 provide a filament or cathode sleeve with a coating which possesses a predetermined distribution of coating material. Thus it may be desired to provide the end regions of a filament or of a cathode sleeve with a thicker'coating than the 60 middle region, while maintaining the coatings in these respective regions uniform. Such a result is obviously unattainable with ordinary spray or cupping processes.

Accordingly, another object of the invention 3 is to provide a method whereby the thickness as well as the uniformity of electron-emissive coating may be accurately controlled.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention will be disclosed in the form of a machine for practising the same it will be obvious that the inventive method can be practised manually or by using apparatus other than that disclosed.

Accordingly, in the drawing Fig. 1 is a perspective view of one preferred embodiment of apparatus for practising the invention.

Fig. 2 is a detail sectional view of part of the mechanism of Fig. 1.

Fig. 3 is a part sectional view of a modified form of coating roller.

Referring to Fig. 1, the numeral l indicates any suitable base upon which the various parts of the machine are supported. Aflixed to base I, for example by screw 2 is a standard 3 which has bolted to its upper' end a guide member 4 through which passes the vertical arm 5 of a cathode supporting frame. Preferably the arm 5 is rectangular in cross section, and the bore of member 4 is likewise rectangular to prevent the frame turning while it is being reciprocated. The said frame is provided with a hollow arm 6 through which passes the rotatable spindle I, the latter having attached to its right hand end a suitable pulley 8, the left hand end of the spindle being provided with 'a head 9. The head 9 is provided with an opening to receive and frictionally retain the member In to be coated. Thus the head! may have fitted into the end thereof a rubber bushing into which the member Ill may be easily inserted and held in axial alignment with spindle 'l. The slidable frame is reciprocable vertically and is normally held in its lowered position by reason of spring H which has one end fastened to standard 3 and the other end fastened to member 6.

For the purpose of raising and lowering the frame there is provided a lever l2 which is pivotally mounted, as for example at l3, in an extension affixed to member 3. Normally spring ll urges the frame downwardly so that the lower end of arm 5 engages the inner end of lever l2, and when it is desired to raise the frame the outer end of said leveris lowered and may be held in its lowered position by means of a suitable'catch l5.

Fastened to base I is another standard l6 having an arm I! on which is supported a reservoir ll containing the coating material II in liquid or semi-liquid form. An inlet pipe 2| supplies the coating material to the reservoir and an overflow pipe 2-! is provided to prevent the liquid rising above a predetermined level. Standam It supports a bearing member 21in which rotates the. spindle 23, said spindle having attached to itsl'ight hand end the grooved roller 24 and at its left hand end the pulley II. The pulleys I and 2l"may be driven from the continuously rotating shaft 26 through respective pulleys 21, 28 and belts 29, 30. Preferably the pulleys are designed so that the spindle I rotates at a higher speed than the spindle 23.

Any known type of electron-emissive coating liquid maybe employed so long as theviscosity and level of the liquid in'the reservoir it are chosen so as to give the desired thickness to the coating. Preferably, although not necessarily,'

the grooves in roller 24 are curved in cross-section but if desired these grooves may be V-shaped.

Preferably also the grooves are designed as recosity of the coating material, each groove carries with it an accurately predetermined amount of coating material, so that when the cathode sleeve is lowered into coating position as indicated in Fig. 2, the material in the grooves is uniformly applied to the sleeve. It will be noted that in order to effect the coating it is not necessary that the cathode sleeve be brought into physical contact with the surface of the roller, since the cathode sleeve is being rotated at relatively high speed and the centrifugal force tends to smooth out any irregularities or striations in the applied coating material and also prevents the formation of beads on the cathode sleeve. When the required amount of material has been applied, the lever i2 is operated to raise the cathode which however continues to rotate until it is removed from the head 9. The coated cathode sleeve after being removed, may be dried or baked in any well-known manner and then packed in suitable containers ready for use.

In some types of electron-emitting devices it is desirable to provide a cathode sleeve with different thicknesses of coating at different parts of the sleeve. This of course is to be distinguished from the haphazard nonuniformity which results from the ordinary spraying or cupping processes. In such types of tubes it is required that the thickness of the coating (even though this thickness may vary along the length of the oathode) should be accurately controlled and should be uniform in large batches of coated sleeves.

-For example in some cases it may be desirable to provide the end regions of the cathode sleeve Y with a thicker coating than the middle region.

portions of the cathode sleeve. It will be clear by centrifugal force.

therefore that the coating on the cathode sleeve may be given any desired and accurately controlled distribution of electron-emissive material, by correspondingly g the shape and size I of the grooves in the roller.

From the foregoing description, it will be seen that there is provided a device which is wellsuited to the complete automatic coating of cathode sleeves. Thus the cathode sleeves may be automatically loaded into the head 9 by any suitable mechanical loading-means (not shown) and the raising and lowering of each cathode sleeve into coating relation with the roller 24 may be automatically timed, so that each sleeve is subjected to the same duration-of coating. At the end of this coating period the cathode sleeve may be automatically discharged from the head ill and carried by a suitable conveyor or the liketo another station where' it may be baked or heated.

Various changes and modifications may be made herein without departing from the spirit and scope of the invention.

This application is a continuation in part of application Serial No. 13,107, filed March 26, 1935, issued as Patent No. 2,069,637.

What I claim is:

1. The method of providing a cathode sleeve for an indirectly heated cathode with an electronemissive coating which includes the steps ofjsupporting the sleeve in spaced relation to the periphery of a coating roller, applying to theperiphcry of the roller a flowable material containing the electron-emissive material, rotating the roller to transfer the material therefrom to said sleeve said material being in contact with the sleeve during rotation of the roller, simultaneously rotating said sleeve about its own axis to distribute the coating uniformly thereon, and subsequently baking the coating'on the sleeve.

2. The method according to claim 1 inwhich the coating roller and the sleeve are rotated at different rotational speeds.

3. The method according to claim 1 in which the sleeve is rotated at a higher rotational speed than the coating roller to distribute the material uniformlythereover by centrifugal force.

4. The method of providing a cathode sleeve for an indirectly heated cathode with an electron-emissive coating which includes the steps of, supporting the sleeve in spaced relation to the periphery of a grooved coating roller, applying a fiowable material containing the electron-emissive material to the roller, rotating the roller to transfer the flowable material to said sleeve said material being in contact with the sleeve during rotation of the roller, simultaneously rotating said sleeve about its own axis, removing said sleeve from the proximity of said roller, continu ing the rotation of the sleeve independently of the roller to distribute the coating on the sleeve by centrifugal force, and subsequently baking the material in a fiowable condition andwith the said material in surface contact with the sleeve while rotating, the rotation of the sleeve serving to distribute the coating material uniformly thereon EDWARD n. wrrrrcn. 

